Case Study: Efficiently Replace PLC Automation Systems by Integrating IEDS with Fiber-Optic and Ethernet Communications in the Substation

Abstract

This paper describes the successful replacement of an existing legacy PLC (programmable logic controller)-based substation automation design with integrated mission-critical protection intelligent electronic devices (IEDs). The new design replaces existing radios and leased-line modems with a hybrid serial and Ethernet local area network (LAN) with wide area network (WAN) connections. The new system exploits the full capabilities of communications processor technology to integrate existing protective relays and meters with new I/O (input and output) processors while also adding Ethernet connectivity to an expansion bay added to an existing substation. The decision to replace the existing PLC-based control system was based primarily on the cost of the existing system, the difficulty of adding new capabilities (such as substation expansion or new communications methods), and inadequate product support. In addition to the high cost of the initial installation, the PLC design required substantial changes to the PLC hardware and software, termination panels and wiring, and field wiring, which made the cost of adding feeders to the existing system prohibitively expensive. Therefore, the primary drivers were to choose a system that was designed to support easy expansion and migration to new communication technologies from a vendor with demonstrated ability to provide timely product support. Perhaps the most important desire was to choose a technology that could be added without ANY disruption to the existing systems. Engineers wanted to add automation to a substation expansion bay without adversely affecting the in-service PLC system controlling the original part of the substation.